function Supermarket() { }
Supermarket.prototype.product = '口罩'

// person.__proto__ === Supermarket.prototype
function Shop() { }
Shop.prototype = new Supermarket()

// person.__proto__ === Shop.prototype
let person = new Shop()
console.log(person.product)


// 一道面试题
let F = function () { }

Object.prototype.a = "jiffy"
Function.prototype.b = function () { }

let f = new F()
console.log(f.a) // 
console.log(f.b)

// f.__proto__ ========> F.prototype ========> Object.prototype